1. Field of the Invention
The present invention relates to a position measuring device and a position measuring method that obtain a position using a triangulation method by receiving reflected light and scattered light of laser light irradiated on a surface of an object to be measured.
2. Description of Related Art
As position measuring devices that measure a position of a surface of an object to be measured in three-dimensional coordinates, there is a contact type position measuring device in which a probe is brought in contact with a surface of the object to be measured, and a non-contact type position measuring device that performs measurement by irradiating laser light on a surface of the object to be measured.
FIG. 10 illustrates a schematic diagram illustrating a non-contact type position measuring device that uses a triangulation method. As illustrated in FIG. 10, the position measuring device includes a light emitter 10 that emits laser light L1 toward an object to be measured OB (hereafter referred to as object OB), and an image capturer 20 that is provided on an optical axis that is non-parallel to an optical axis of the laser light L1. To measure a position of the object OB, the laser light L1 is emitted from the light emitter 10 toward the object OB, and scattered light of the laser light L1 at the object OB is captured by the image capturer 20. In the position measuring device, a disparity D is provided between the light emitter 10 and the image capturer 20. Therefore, based on position information Lx captured by the image capturer 20, a focal distance f and the disparity D, a displacement L of the object OB can be obtained using the triangulation method. Although the illustration in FIG. 10 is simplified, it is preferable that an optical system use a Scheimpflug optical system.
In such a non-contact type position measuring device, Japanese Patent Laid-Open Publication No. 2002-139311 discloses a configuration in which, based on an amount of light received of reflected light that is detected by a photosensor, an intensity of a light beam from a light beam radiator is corrected and an amount of light received by a line sensor is kept constant. That is, in the position measuring device described in Japanese Patent Laid-Open Publication No. 2002-139311, in order to improve measurement accuracy, control is performed so that an amount of light received is fed back to adjust an intensity of a light beam, and an amount of light captured by the line sensor is kept constant.
In a case where a predetermined angle is provided between the optical axis of the laser light and the optical axis of the image capturer as in the position measurement using the triangulation method, when there is an interfering object of some kind on the optical axis of the image capturer, a shadow is formed and it becomes impossible to receive enough diffused light. As described above, that diffused light being blocked from an object to be measured is blocked is referred to as “occlusion.”
FIG. 11 illustrates a schematic diagram illustrating a state in which the occlusion is occurring. As illustrated in FIG. 11, in the case where the laser light L1 emitted from the light emitter 10 along a first optical axis a1 is irradiated on the object OB and the diffused light of the laser light L1 is captured by the image capturer 20, when there is another object OB2, for example, on a second optical axis a2 of the image capturer 20, a shadow is formed. Here, in the position measuring device described in Patent Literature 1, when such occlusion has occurred, in response to decrease in the amount of light received, feedback control is performed to increase the intensity of the laser light L1. As a result, the decrease in the amount of light received by the image capturer 20 is compensated.
However, when the occlusion is resolved in the state in which the intensity of the laser light L1 has been increased, more than necessarily intense diffused light is generated and the amount of the diffused light captured by the image capturer 20 becomes too large. When the amount of light received by the image capturer 20 is too large, a measurement result is affected and this becomes a factor causing accuracy of the position detection to decrease.
Further, FIGS. 12A and 12B respectively illustrate schematic diagrams of a state in which laser light is not irradiated on an object to be measured and a state in which the laser light is irradiated on the object to be measured. As illustrated in FIG. 12A, when the laser light L1 deviates from the object to be measured and propagates toward an open space, diffused light is not generated from the object OB. In such a case, since the amount of the diffused light received by the image capturer 20 is small, control to increase the intensity of the laser light L1 is performed.
However, as illustrated in FIG. 12B, when a measurement point moves so that the laser light L1 is irradiated on the object OB, the laser light L1 of a high intensity is temporarily irradiated on the object OB, and intense diffused light is generated. In particular, the diffused light is intensely generated at an edge part of the object OB. By receiving this very intense diffused light, the amount of light received by the image capturer 20 is likely to cause overflow.